Vehicles have become more and more automated to accommodate the desires of consumers. Vehicle parts, including windows, sun roofs, seats, sliding doors, and lift gates (e.g., rear latches and trunks) have been automated to enable users to press a button on the vehicle or on a remote control to automatically open, close, or otherwise move the vehicle parts.
While these vehicle parts may be automatically controlled, the safety of consumers and objects is vital. An obstacle, such as a body part or physical object, that obstructs a vehicle part while closing could be damaged or crushed, or the vehicle part or drive mechanism could be damaged, if the obstacle is not detected while the vehicle part is moving.
In the case of detecting obstacles in the path of an automatic lift gate or other closure system, one conventional technique for speed control and sensing an obstacle has been to use Hall Effect sensors or optical vane interrupt sensors. The Hall Effect sensors or optical vane interrupt sensors are positioned in a motor or on a mechanical drive train. Sensor signals are generated by the rotation of the motor giving velocity to the drive mechanism. The sensor signals can be used to detect a change in velocity and to allow for speed control and obstacle detection. This sensing technique is generally known as an indirect sensing technique.
One problem with the use of Hall Effect sensors and optical vane interrupt sensors is a result of mechanical backlash due to system flex and unloaded drive mechanism conditions. As an example, when a lift gate is closing, the gate reaches a point where the weight of the lift gate begins to close the lift gate without any additional effort from the drive mechanism. In fact, at this point, the drive mechanism applies effort to the lift gate to prevent premature closing. This is a state when negative energy is imparted from the drive mechanism to the lift gate. In order to detect an obstacle at this point, the drive mechanism must transition from a negative energy state to a positive energy state. Once the transition to the positive energy state occurs, a controller of the drive mechanism can then detect a change in the velocity of the drive mechanism, thus detecting a collision with an obstacle. The controller may then signal the motor to change direction. The obstacle detection process may take hundreds of milliseconds to complete, which is too long to detect a sudden movement of the lift gate and long enough to cause injury to a person or damage to an object, vehicle part, or drive mechanism. As a result, obstacle detection is very difficult at the end of travel when sensitivity to obstacles should be the highest to avoid damaging obstacles or damaging the vehicle part.